docs: def processCheckIn(request):
      '''
      This function handles the Ajax call made when a user is marked as checked in
      '''
  
      if request.method == 'POST':
          event_id = request.POST.get('event_id')
          reg_ids = request.POST.getlist('reg_id')
  
          if not event_id:
              return HttpResponse(_("Error at start."))
  
          # Get all possible registrations, so that we can set those that are not included to False (and set those that are included to True)
          all_eventreg = list(EventRegistration.objects.filter(event__id=event_id))
  
          for this_reg in all_eventreg:
              if str(this_reg.registration.id) in reg_ids and not this_reg.checkedIn:
                  this_reg.checkedIn = True
                  this_reg.save()
              elif str(this_reg.registration.id) not in reg_ids and this_reg.checkedIn:
                  this_reg.checkedIn = False
                  this_reg.save()
          return HttpResponse("OK.")